Plastic lens mounting for varifocal objective

ABSTRACT

A stationary outer lens barrel slidably receives a movable inner lens barrel serving to support two axially displaceable components of a varifocal objective in interleaved relationship with two fixed components supported in the outer lens barrel. One of the fixed components, i.e. the rearmost component of the fourcomponent varifocal group, is seated on a fixed internal abutment of the outer lens barrel; the other fixed component, i.e. the second from the front, is carried on an insert which is guided in axial wall slots of the inner lens barrel and is snapped into recesses on the inner wall surface of the outer lens barrel before the movable front lens is positioned in its seat on the inner lens barrel.

[ Apr. 15, 1975 United St Kulle et al.

PLASTIC LENS MOUNTING FOR VARIFOCAL OBJECTIVE Agent,

[75] Inventors: Elfriede Kulle, Waake; Rolf Meyer,

Gottingen, both of Germany ABSTRACT A stationary outer lens barrelslidably receives a movm Ha m a 0 e! n we Wn m M0 m e Ofi m IG e n .m SS A H 7 [22] Filed: 1973 able inner lens barrel serving to support twoaxially displaceable components of a varifocal objective in [211 App].No.: 414,826

interleaved relationship with two fixed components supported in theouter lens barrel. One of the fixed [30] Foreign Application PriorityData Nov. 10, 1972 Germany...........................

components, i.e. the rearmost component of the fourcomponent varifocalgroup, is seated on a fixed inter- 707 8 8 m w 5%5 W mm .c Hr .e

i UhF HUN 555 inner lens barrel and is snapped into recesses on theinner wall surface of the outer lens barrel before the movable frontlens is positioned in its seat on the inner lens barrel.

References Cited UNITED STATES PATENTS 3 582188 Rau et al 350/187 x3,748,024 7 1973 Rodier et 350/187 x 10 Clams 4 D'awmg FguresPATENTEUAPR 1 5197s sum 2 0F 2 FIG. 3

FIG. 4

PLASTIC LENS MOUNTING FOR VARIFOCAL OBJECTIVE FIELD OF THE INVENTION Ourpresent invention relates to a mounting for a plurality of lenses whichare relatively movable in axial direction. more particularly for a pairof fixed components and a pair of axially movable components formingpart of a varifocal lens group.

BACKGROUND OF THE INVENTION Varifocal lens groups of this descriptionare frequently designed as separate attachments for a basic objective ina camera or a projector. the relative slidability of the fixed andmovable components thereof serving to vary the overall focal length ofthe resulting system. In cases where the two movable components arebracketed by the two fixed components. the position of the stationaryfront lens may be limitedly adjustable for focusing purposes. In otherinstances. especially with a movable front component. focusing may beaccomplished by an axial shift of the entire group.

OBJECTS OF THE INVENTION The general object of our present invention isto provide a lens mounting for such a varifocal group which is of simpleconstruction. may be mass-produced from plastic material by injectionmolding. and can be conveniently assembled.

A more particular object is to provide a mounting specifically designedfor a four-component varifocal group whose first and third components(counted from the front or object side of the system) are movable whileits second and fourth components are stationary.

with bodily mobility of the entire group for focusing purposes asmentioned above.

SUMMARY OF THE INVENTION We realize these objects. in conformity withour present invention. by the provision of two nested and relativelyaxially slidable lens barrels. i.e. an outer lens barrel with a rear endforming a seat for the fourth component and an inner lens barrel formingtwo axially spaced seats for the first and third components of thegroup; an insert. comprising a central ring with a plurality of axiallyextending legs peripherally secured thereto. forms a seat for thestationary second component. the legs of this insert being slidablyreceived in peripherally spaced wall slots of the inner lens barrelextending axially from the front end thereof. The insert. with itssecond component is introduced into the inner lens barrel through itsopen front end before the first component is cmplaced; upon subsequentimmobilization of that insert with reference to the outer lens barrel bysuitable fastening means. this first component is placed on its seat andsecured in position on the inner lens barrel by suitable means.preferably by a detachable head threadedly secured to a front flange ofthat barrel.

The immobilization of the insert advantageously is achieved by aligningthe wall slots of the inner lens barrel with respective recesses on theinner wall surface of the outer lens barrel and letting projections onthe legs of the insert snap into these recesses behind overhangingshoulders provided at their forward ends.

LII

BRIEF DESCRIPTION OF THE DRAWING The above and other features of ourinvention will now be described in detail with reference to theaccompanying drawing in which:

FIG. I is an exploded perspective view. with parts broken away. of theseveral constituents of a lens mounting according to our invention:

FIG. 2 is a cross-sectional view taken on the line Il--ll of FIG. 1:

FIG. 3 is an axial sectional view ofthe assembled lens mounting in oneextreme working position. taken on the line III-III of FIG. 2; and

FIG. 4 is a view similar to FIG. 3. showing the assembly in its otherextreme working position.

SPECIFIC DESCRIPTION The lens mounting shown in the drawing consists ofan outer lens barrel 1. an inner lens barrel 2. and insert 16 fittinginto the latter lens barrel. and a head 15 threadedly engageable withthe same lens barrel. All these constituents are made from plasticmaterial by conventional injection molding.

The outer lens barrel 1 has a solid peripheral wall. of generallycylindrical configuration. with an enlarged forward extension I7 andwith a rear wall 18 forming a seat for a compound lens 9 representingthe fourth or rearmost component of a varifocal lens group as describedabove. The inner wall surface of barrel I is provided. at locationsperipherally spaced apart by I20". with shallow recesses 13 of limitedaxial length. each recess terminating at its front in a transverse notch14 overhung by a shoulder 20. In the assembled condition of the unit.illustrated in FIGS. 3 and 4. longitudinal slots 5 in the wall of innerlens barrel 2 are respectively aligned with the recesses I3: these wallslots extend rearwardly from a peripheral front flange 2I of barrel 2whose outer diameter exceeds the inner diameter of barrel 1. Flange 21is peripherally recessed at 22 to form a seat for a lens 6 serving asthe first component of the varifocal group. Another lens 8. constitutingthe third component of that group. is fixedly held in a seat 23 at therear end of lens barrel 2. The wall of this lens barrel is split in theregion of lens 8 into an inner ring 2a and an outer ring or skirt 2b.the two rings being partly divided into segments by the slots 5 whichterminate at section line IIII. i.e. at the level of the forward face ofseat 23. to form end stops 24 engageable with the insert 16 in anextended position (FIG. 4) of barrel 2. The skirt 2b is furthersubdivided by longitudinal slots 4 midway between channels 5. Thissubdivision results in the formation of three pairs of arcuate flapswhich are inherently biased outwardly toward the wall of the surroundinglens barrel 1; longitudinal ribs 3. extending over the full length ofthe cylindrical outer peripheral wall of lens barrel 2 including theskirt 2b. define limited zones of surface contact between the two lensbarrels to facilitate their relative axial displacement between theretracted position of FIG. 3 and the extended position of FIG. 4.

Insert 16 comprises a central ring 10 and three peripherally spaced legs11 which are generally L-shaped. their shorter radial portions servingto secure their longer axial portions to the ring. These axial portionsare slidably received in the slots 5 of barrel 2 and. upon assembly.enter the respective recesses 13 of barrel 1. Such assembly occursbefore emplacement of the front lens 6. thus enabling the insert 16 tobe driven rearwardly until stops 12 on its legs 11 snap into thetransverse notches H of the associated recesses 13. This immobilizes theinsert 16. together with a lens 7 mounted in its ring l0. with referenceto the outer barrel 1. Thereafter. lens 6 is put into place on its seat22 whereby lens 7 is sandwiched between lenses 6 and 8 as the secondcomponent of the group.

To complete the assembly. and to lock the lens 6 in position. head 15 isscrewed into flange 21 by means of male threads 25 engagingcomplementary female threads 26 of that flange. The head 15 then alsoserves as a convenient means for axially shifting the lens barrel 2 withits movable components 6 and 8 relatively to the lens barrel 1 with itsstationary components 7 and 9'. the engagement of legs 11 with slots 5and recesses 13 prevents relative rotation of the two lens barrels. lnthe position of FIG. 4, the stops 24 forming the rear ends of slots 5come to rest against the radial portions of legs 11.

The entire assembly. shown in FIGS. 3 and 4. may be inserted into a boreof a nonillustrated objective holder such as. for example. a projectorhousing. To facilitate focusing. the outer wall surface of lens barrel 1may be helically threaded to mate with complementary threads on theholder.

The described lens mounting requires no aftertreatment following themolding operation. nor additional hardware for securing the lenses inposition. The material used for its parts may be suitably pigmented togive a mat-black appearance. thereby minimizing reflections at the innerwall surfaces; this latter feature has been claimed in a commonly ownedapplication. filed on even date herewith by Lothar HUMMEL. which alsoshows the threading of a molded lens barrel into a holder therefor.

Naturally. the plastic material used especially for the insert 16 shouldhave sufficient elasticity to facilitate the aforedescribed snap-actionassembly. The lenses. or some of them. could be provided with metallicretaining rings as indicated at 27 for component 7.

We claim:

1. A mounting for a four-component varifocal lens group including amovable first component. a fixed second components. a movable thirdcomponent and a fixed fourth component. comprising:

an outer lens barrel with a rear end forming a seat for said fourthcomponent. said outer lens barrel having an inner wall surface with aplurality of peripherally spaced recesses bounded at the front byoverhanging shoulders;

an inner lens barrel slidably telescoped in said outer lens barrel. saidinner lens barrel forming two axially spaced seats for said first andthird components and being provided with a plurality of peripherallyspaced wall slots in line with said recesses extending axially from afront end thereof; an insert comprising a central ring with a pluralityof axially directed legs with forwardly extending free ends peripherallysecured to said ring. said legs being received in said wall slots and inthe recesses of said outer lens barrel aligned therewith. said ringforming a seat for said second component; and

fastening means for immobilizing said insert with reference to saidouter lens barrel. said fastening means including outer projections onsaid legs near their free ends received with a snap fit in said recessesin contact with said shoulders.

2. A mounting as defined in claim 1 wherein said inner lens barrel isprovided with a peripheral front flange having an outer diameter largerthan the inner diameter of said outer lens barrel. said wall slotsterminating at said flange.

3. A mounting as defined in claim 2, further comprising a steppedannular head threadedly secured to said flange. said head projectingforwardly from said outer lens barrel to facilitate manipulation of saidinner lens barrel.

4. A mounting as defined in claim 3 wherein said head coacts with themore forward one of said axially spaced seats to lock said firstcomponent in position.

5. A mounting as defined in claim 3 wherein said lens barrels. saidinsert and said head consist of plastic material.

6. A mounting as defined in claim 1 wherein said inner lens barrel isprovided with a set ofexternal longitudinal ribs contacting the innerwall surface of said outer lens barrel to facilitate relative sliding.

7. A mounting as defined in claim 6 wherein said inner lens barrel has arearwardly facing skirt with peripheral slits dividing same intooutwardly biased segments. said ribs extending over said segments.

8. A mounting as defined in claim 7 wherein said slits are peripherallyinterleaved with said ribs.

9. A mounting as defined in claim 1 wherein said legs are substantiallyL-shaped and have radially extending portions secured to said ring.

10. A mounting as defined in claim 9 wherein slots terminate in stopsengageable by said radially extending portions in an extended positionof said inner lens barrel.

1. A mounting for a four-component varifocal lens group including amovable first component, a fixed second components, a movable thirdcomponent and a fixed fourth component, comprising: an outer lens barrelwith a rear end forming a seat for said fourth component, said outerlens barrel having an inner wall surface with a plurality ofperipherally spaced recesses bounded at the front by overhangingshoulders; an inner lens barrel slidably telescoped in said outer lensbarrel, said inner lens barrel forming two axially spaced seats for saidfirst and third components and being provided with a plurality ofperipherally spaced wall slots in line with said recesses extendingaxially from a front end thereof; an insert comprising a central ringwith a plurality of axially directed legs with forwardly extending freeends peripherally secured to said ring, said legs being received in saidwall slots and in the recesses of said outer lens barrel alignedtherewith, said ring forming a seat for said second component; andfastening means for immobilizing said insert with reference to saidouter lens barrel, said fastening means including outer projections onsaid legs near their free ends received with a snap fit in said recessesin contact with said shoulders.
 2. A mounting as defined in claim 1wherein said inner lens barrel is provided with a peripheral frontflange having an outer diameter larger than the inner diameter of saidouter lens barrel, said wall slots terminating at said flange.
 3. Amounting as defined in claim 2, further comprising a stepped annularhead threadedly secured to said flange, said head projecting forwardlyfrom said outer lens barrel to facilitate manipulation of said innerlens barrel.
 4. A mounting as defined in claim 3 wherein said headcoacts with the more forward one of said axially spaced seats to locksaid first component in position.
 5. A mounting as defined in claim 3wherein said lens barrels, said insert and said head consist of plasticmaterial.
 6. A mounting as defined in claim 1 wherein said inner lensbarrel is provided with a set of external longitudinal ribs contactingthe inner wall surface of said outer lens barrel to facilitate relativesliding.
 7. A mounting as defineD in claim 6 wherein said inner lensbarrel has a rearwardly facing skirt with peripheral slits dividing sameinto outwardly biased segments, said ribs extending over said segments.8. A mounting as defined in claim 7 wherein said slits are peripherallyinterleaved with said ribs.
 9. A mounting as defined in claim 1 whereinsaid legs are substantially L-shaped and have radially extendingportions secured to said ring.
 10. A mounting as defined in claim 9wherein slots terminate in stops engageable by said radially extendingportions in an extended position of said inner lens barrel.